Improvements in the cure rate of cancer by current treatments, including radiotherapy and chemotherapy, depend on exploiting some difference between normal and malignant tissues. One such difference is their level of oxygenation: human solid tumors are on average poorly oxygenated compared to normal tissues because of their inadequate vascularization to tumors is currently a negative prognostic factor, it could also be exploited if a drug that is activated to a cytotoxic species only under low oxygenation could be added to standard therapy. Tirapazamine (TPZ), a drug preferentially metabolized under hypoxia, is the first drug to enter clinical trials to test this rationale. Importantly, it has proven effective in Phase II and II clinical trials when combined with the ant-cancer drug, cisplatin. However, the efficacy of TPZ is limited by its systemic toxicity, particularly when combined with radiotherapy. We have recently discovered a number of features of the enzymology and toxicity of TPZ as well as developed new assays that could potentially be exploited in development of analogs of TPZ designed to maximize anti- tumor efficacy and minimize systemic toxicity. This Program Project combines the efforts of three laboratories with extensive experience in the design, synthesis and testing of hypoxia-activated cytotoxic compounds, including TPZ. The goal of the collaboration will be apply these newly discovered features and assays, as well as the extensive knowledge gained of factors affecting the efficacy and toxicity of hypoxic cytotoxins, to develop optimum second generation TPZ analogs for use with fractionated radiation and for use with cisplatin-based chemotherapy.